Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
Case	Tag   Price	Sales   Tax %	Raw Total   Incl. Sales Tax	Rounded   to Penny	Rounded   to Nickel	Rounded   to Dime
Purchase #1	$123.31	13.299%	$139.709	$139.71	$139.70	$139.70
Purchase #2	$130.46	10.874%	$144.6462	$144.65	$144.65	$144.60
Purchase #3	$79.42	11.181%	$88.3	$88.30	$88.30	$88.30
Purchase #4	$175.36	11.783%	$196.0227	$196.02	$196.00	$196.00
Purchase #5	$136.69	5.573%	$144.3077	$144.31	$144.30	$144.30
Purchase #6	$59.27	5.837%	$62.7296	$62.73	$62.75	$62.70
Purchase #7	$96.43	13.841%	$109.7769	$109.78	$109.80	$109.80
7 purchase totals =	$800.94		$885.4921	$885.50	$885.50	$885.40